Rope Rescue
Multi Point Force Distributing Anchor

In rope rescue we owe teammates our experience and expertise, and also as instructors and team leaders, we have a requirement to maintain an open mind towards new safety systems as they evolve. Further, we must avoid over-complicating the systems while striving for higher safety standards. The debate in regards to M.P.F.D.A. vs. integral (non-force distributing) anchors is not new and is an ongoing, yet interesting dilemma.

In 1991, Ian Stewart-Patterson and Murray Toft issued a paper taking a different approach to M.P.F.D.A. and offering what appears to be a better solution. Their paper demonstrates broad minded sound research and what I have done is apply several types of belay devices, being curious about results, which appear to have improved the original setup. Before we go into the additions/improvements in depth, let us examine advantages and disadvantages of the two basic anchor loop systems.

Integral anchor loops

Advantages: Basically they are anchor loops clipped together at a common "master point of attachment" carabiner, easy to tie and set up, simple to understand, minimal secondary shock load.

Disadvantages: Only one anchor truly holds the entire load thus making the system susceptible to "zippering" type failure.There is no distribution of the load among several anchors; it is non-directional.

Multi Point Force Distributing Anchors

Advantages: Distributes the overall load, as its name implies, over several anchors, each taking a portion of the load. It can be quickly shifted and directed, thus set over 180' degree of radius.

Disadvantages: The load cannot be truly equalized, some anchors hold more of the load than others. If anchor failure occurs, secondary shock loading may result in varying degrees of severity, as the load redistributes itself among the remaining anchors. The M.P.F.D.A. requries more skill at rigging.

So in a compromise between the two systems, a safe creation using the Stewart-Patterson, Toft concept has resulted in what appears to be a good, safe, innovative, load distributing anchor. Further testing by those with access to facilities is still needed though.

At this time the belayed M.P.F.D.A. appears to be an advancement that testing will either discount or verify. As the drawing above demonstrates, the load is belayed by the friction hitches when anchor failure occurs. One qualification must be made though.... If a two point anchor system is used a Munter hitch is acceptable. If more than two anchors are used, the "floating carabiner" device by Robert Chisnall is more appropriate.

The mode it sits in, on a M.P.F.D.A., will dissipate higher loads than a Munter hitch in a safer manner. When a Munter is used with more than two anchors, the hitches cause somewhat of a "traffic jam", abutting each other during anchor failure. One other belay device which is quite suitable is the "Chisnall Carabiner Wrap" which, if necessary, can be locked completely off with the "Chisnall-Fillion Belay hitch", resulting in integral anchor if the situation requires.

Note: When anchor failure takes place the floating carabiner shifts belay mode from most dynamic to least dynamic as run through takes place - this is a definite advantage - dissipating the load gradually rather than stopping it instantly and risking the dreaded shock load.

Expected belay capacity of the aforementioned belay device: the Munter hitch load capacity may self adjust from: 290-320 lbs (131-144 kg) to 520-590 lbs (234-266 kg) per device.

Chisnall floating Carabiner load capacity may self adjust from: 270-370 lbs (122-135 kg) to 400-420 lbs (189-207 kg) per device.

Carabiner wrap load capacity may self adjust from: 340-370 lbs (153-167 kg) to 400-420 lbs (180-189 kg).

Note: Any of these Chisnall wraps can be used as a belay device for rescue loads, outside the MPFDA.

Considering that in a three point anchor setup two belay devices come into play, the load slowing / dissipating capacity is greatly increased while secondary shock loading may be decreased to a safe acceptable, or possibly non-existant level. It is to be emphasized that while the belay devices mentioned are all time tested and proven (ref: O.R.C.A. manual) their capacity in M.P.F.D.A.'s is still in development. In addition to this - 8mm prussik loops on 11mm rope in M.P.F.D.A.'s may yet play a role (ref: "Are you really on belay" by John Dill). These, in combination with belay devices on M.P.F.D.A.'s, may solve the age old problem and end the debate, which in this case, along with necessity, has proved to be the mother of invention.

Let us know at SARBC of any test results you may obtain with the belayed M.P.F.D.A. setup.

Reference

• "A Shock to the System", Ian Stewart-Patterson and Murray Toft; University of Calgary, Alberta, Canada. 1991
• Ontario Rock Climbing Assoc. Safety Manual 2nd Edition; Ministry of Culture, Tourism and recreation, 1989; Queens Park, Toronto, Ontario, Canada
• M.P.F.D.A.'s - Combinations (manuscript in progress) 1995; by J. Danis
• Urban Rope Entry Systems - by J. Danis; Shadowgraghics Publications 1994, Victoria B.C. Canada; also available through SARBC
• Are you really on Belay - by John Dill; Response Magazine 1990
• Does the munter hitch measure up? 1994; Rescue magazine Sept/Oct 1994; Norman King and Richard Wright